(1) Field of the Invention
The present invention relates to a transmission/reception system, and in particular to a technique for preventing unauthorized use of contents in contents distribution.
(2) Related Art
In recent years, home networks have started to become a reality. In such networks, devices in a home which are connected over the network share contents. One form of such a home network is one in which devices such as a server, televisions, and audio devices are connected in a star formation around a central hub. The hub is connected to a router which is the only device in the home to be connected to an external network. The server stores various contents, which it obtains from the external network via the hub and the router, and then distributes the contents to the devices in response to requests from the devices. This enables the devices to share the various contents.
However, unlimited sharing of contents is unacceptable from the point of view of rights protection. Consequently, contents that are permitted to be used only by devices in the home must be restricted so that they are not distributed to external devices. (Hereinafter, “authorized domain” (AD) is used to denote the limited range within which contents are permitted to be shared). For this reason, when the server receives a request for contents distribution from a device, it is necessary for the server to confirm that the device is within the AD, before distributing the contents to the device.
Japanese unexamined patent application publication No. 2001-285284 discloses a method that focuses on IP (Internet protocol) network addresses. In this method, a server judges whether the network address of a device that has requested distribution of contents is the same as the network address of the server, and recognizes the device as being in the AD when the network addresses are the same.
However, since network address settings can be easily changed with the user interface, a malicious user can register the AD network address in an external device. When a distribution request is received from such an external device, the server recognizes the external device as being within the AD and distributes the contents to the external device. Consequently, distribution of contents to devices outside the AD is unable to be restricted.